1. Field of the Invention
The present invention relates generally to an autofocus lens barrel attached to a camera etc and, more particularly, to a technology capable of easily and precisely controlling a torque between a manual focus ring and a connecting member.
2. Related Background Art
A camera is fitted with various types of lens barrels which may be exemplified by, as a beginning, a unifocal lens barrel and a zoom lens barrel, and further a wide-angle lens barrel and a telephoto lens barrel etc. The lens barrel includes a plurality of lens units each consisting of a single or a plurality of optical lenses, and focusing is executed by properly changing a relative distance between the lens units. In recent years, a so-called autofocus camera among the cameras in a comparatively low price zone has an autofocus mode in which the focusing is implemented by the camera itself in addition to a manual focus mode in which a photographer himself or herself performs the focusing by rotating a manual focus ring provided on an outer peripheral surface of the lens barrel, and therefore widely prevails.
In the autofocus camera, the camera body incorporates a focusing control device composed of a microcomputer and a CCD sensor etc, wherein an electric motor incorporated in the lens barrel or the camera is rotationally driven corresponding to a distance to a subject, and a rotational force thereof is transmitted to a focusing optical system moving device in the lens barrel. The focusing optical system moving device is, though various types of focusing optical system moving devices are known, as illustrated in FIG. 6, in most cases constructed of a focus rotary lever 61 fixed to a rotor holder 39 of an electric motor (a ultrasonic motor) 31, and a lens unit holding ring 17 connected via a cam mechanism 101 to the focus rotary lever 61. In this type of lens barrel, upon supplying the ultrasonic motor 31 with a drive current when in autofocusing, the focus rotary lever 61 rotates together with the rotor 41 (and the rotor holder 39 as well), and the lens unit holding ring 17 moves back and forth with an operation of the cam mechanism 101. Note that the ultrasonic motor 31 is rotatably fitted on an outer peripheral surface of an inner fixed drum 15, and frictionally engages with the inner fixed drum 15 with a predetermined slide torque in order to resist reaction given when driving the lens unit holding ring 17. Referring to FIG. 6, the numeral 67 designates a stopper for restricting a rotation of the focus rotary lever 61, and reference symbol L represents an optical axis.
On the other hand, the manual focus ring 7 is rotatably fitted on an outer fixed drum 11, and a connection ring 83 is brought into contact with a rear edge surface of the manual focus ring 7 through a wave washer 103. A pair of inner and outer adjustment screw rings 105, 107 are provided at a rear portion of the connection ring 83. A rear end face of the inner adjustment screw ring 105 is in contact with rollers 109 held at an outer face of a stator holder 35. In FIG. 6, a member designated by the numeral 111 is a spacer for regulating a relative distance of both the adjustment screw rings 105 and 107. The rollers 109 each is in contact with the inner adjustment screw ring 105 at a front face and with a front end face of a rear fixed cylinder 113 at a rear face. Accordingly, if the photographer rotates the manual focus ring 7, the rollers 109 roll along the front end face of the rear fixed cylinder 113, whereby the ultra sonic motor 31 and the focus rotary lever 61 rotate to perform a manual focusing. The manual focus ring 107, which is in friction contact with the connection ring 83 by a spring force of the wave washer 103, is so set that a slide torque thereof is larger than that between the ultrasonic motor 31 and the inner fixed cylinder 15.
The conventional autofocus lens barrel has a problem that an adjustment of a slide torque between the manual focus ring 7 and the connection ring 83 is difficult, which causes reduced production efficiency as well as increased production cost.
The slide torque between the manual focus ring 7 and the connection ring 83 has been adjusted by changing the height of the compressed wave washer 103 (that is, a gap t between the manual focus ring 7 and the connection ring 83), in accordance with the following procedures. First, a spacer 111 having a standard thickness is used and the inner and outer adjustment rings 105, 107 are fastened and positioned, thereafter the ultrasonic motor 31, the rear fixed cylinder 113 and others are assembled provisionary. Next the manual focus ring 7 is rotated to conduct the tests that the ultrasonic motor rotates smoothly within the focus region and that the ultrasonic motor 31 does not rotate after the focus rotary lever 61 is brought in contact with the stopper 67. The former test is for confirming the function of the manual focus ring 7, and the latter test is for preventing damage of the ultrasonic motor 31. In more detail, in the case where the ultrasonic motor 31 rotates even after the focus rotary lever 61 is brought in contact with the stopper 67, the stator 37 will make a relative rotation to the rotor 41 stopped with the focus rotary lever 61, which will damage the contacting surfaces of both of them and remarkably reduce the life of the ultrasonic motor 31.
Upon confirming inconvenience in both of tests, an assembly worker removes a rear fixed drum 113 and the ultrasonic motor 31 out of the lens barrel, and thereafter exchange a spacer 111 by pulling the adjustment screw rings 105, 107 out. This operation, however, requires a great number of steps and much time. Further, the assembly worker, after exchanging the spacer 111, again performs the above test by tentatively assembling the lens barrel once again. If the inconvenience is not obviated, however, the rear fixed drum 113 and the ultrasonic motor 31 must be repeatedly attached and detached. The present inventors made an attempt to reduce a dimensional tolerance of each of the parts in order to solve this problem. This could not, however, be attained because of a large number of components of the ultrasonic motor 31.